Burner

ABSTRACT

A burner for gaseous fuels, e.g. methane or hydrogen, has a porous exit sheet adjacent to a base plate. The two sheets are perforated to allow the passage of air, and fuel gas circulates between the sheets and around the perforations. The fuel passes through the porous sheet to burn with air passing through the perforations.

United States Patent 1191 Desty [4 Apr. 3, 1973 54] BURNER 1,488,677 41924 Hoffman ..431/346X 3 s 'W d e, 3,367,149 2/1968 Manske [75]Inventor f iz enry e y g 491,226 2/1893 Roberts g 2,227,899 1/1941 Grubb3,173,470 3/1965 Wri m [73] Asslgneez The British Petroleum Company3,198,240 8/1965 Keitgh etalm Llmlted, London England 3,437,416 4/1969Saponara ..431/329 [22] Filed: May 1, 1970 [21] Appl. No.: 33,672

[30] Foreign Application Priority Data May 19, 1969 Great Britain..25,4l9/69 [52] US. Cl. ..43l/328, 239/145, 239/425.5 [51] Int. Cl..F23d 13/12 [58] Field of Search ..43l/326, 328, 329; 126/39 1, 126/92B; 239/145, 419.5, 424, 425.5

PrimaryExaminer-Carroll B. Dority, Jr. Attorney-Morgan, Finnegan, Durham& Pine [5 7] ABSTRACT A burner for gaseous fuels, e.g. methane orhydrogen, has a porous exit sheet adjacent to a base plate. The twosheets are perforated to allow the passage of air, and fuel gascirculates between the sheets and around the perforations. The fuelpasses through the porous sheet to burn with air passing through theperforations.

[56] References Cited 5 c1 2 n F UNITED STATES PATENTS 3,147,545 9/1964Valyi ..29/42l 2,194,208 3/1940 Moran ..263/DIG. 5

FUEL

PATENTEDAPR3 I975 3,724,994

FUEL I AIR INVENTORZ DEN|S HENRY DESTY His Attorneys BURNER Thisinvention relates to a burner and in particular to a burner which canburn both high flame speed gases (e.g., hydrogen or towns gas) and lowflame speed gases (e.g., methane).

According to the invention a burner for gaseous fuels comprises aperforated porous exit sheet,e.g., a sheet of metal foam, one side ofwhich is adjacent to a combustion zone and the other side of which isadjacent to a perforated base plate to which the exit sheet is connectedin such a manner that:

a. The perforations in the exit sheet mate with the perforations in thebase plate so as to allow air to pass through them and b. The exit sheetis spaced apart from the base plate between the perforations so as toform fuel passages whose resistance to the flow of fuel gas is lowcompared with the flow resistance through the exit sheet, the exit sheetbeing joined to the base plate along the sides of the fuel passages soas to prevent excessive escape of gas through the joints, the wholeconfiguration being such that, during the use of the burner, gaseousfuel passes throughout the fuel passages and thence via the porous exitsheet into the combustion zone where it burns with air drawn through theperforations.

The configuration specified above is particularly suitable for thinburners, e.g., those less than 10 mm, preferably less than 5 mm, thick.

Preferably the perforations are arranged in an hexagonal pattern and thefuel passages extend throughout the interstitial space between theperforations.

In order to achieve uniform air distribution it is desirable that theair holes be uniformly distributed over the burner. The air holes arepreferably circular in shape and preferably of an area of 0.01 1 cm. Thenumber of air holes is such that they account for 20 50 percent,preferably 25 35 percent, of the total area of the burner.

The invention will now be described by way of example with reference tothe accompanying drawings in which:

FIG. 1 is a plan view of a burner according to the invention, and

FIG. 2 is a cross-section, on an enlarged scale, taken along the line 22of FIG. 1 through one air hole.

The burner takes the form of a thin sheet and, as can be seen from FIG.1, the burner is pierced by perforations arranged in an hexagonalpattern. Fuel passages extend throughout the interstital space 11between the perforations 10.

As can be seen from FIG. 2 the burner is formed from an exit sheet 12and a base plate 13 which are spaced apart from one another between theperforations 10 so as to form fuel passages 14. A joint 15, between theexit sheet 12 and the base plate 13, extends along the sides of the fuelpassages 14. (It is equally correct to state that the joint 15 extendsaround the perimeter of each perforation 10.) The joint can be formed bysuitably folded seams, or by the use of adhesives (e.g., solder) or by acombination of the two.

The exit sheet 12 varies in thickness between 0.5 and 1.0 mm and it ismade of metal foam crushed in the ratio 3:1 (i.e., it was about 3 mmthick originally). The base plate is a metal sheet about 0.5 mm thick.Before crushing the metal foam took the form of a three dimensionalnetwork of tubular nickel strands which defined dodekahedral pores ofaverage diameter 0.3 mm. The crushing flattened the original pores sothat they became thin (about 0.1 mm) in the direction of crushing.

(Irregular dodekahedra can pack to fill space and the foam can beregarded as an example of such a packing. From this point of view themetal strands form the edges of the dodekahedra.)

The thickness of the burner was 5 mm. Each perforation had a diameter of4 mm and the distance between the centers was 8 mm.

During the use of the burner fuel gas passes throughout the fuelpassages 14 and, because their resistance is lower than that of the exitsheet 12, a uniform flow of fuel through the exit sheet 12 into thecombustion zone is achieved. Since it is intended that fuel shall escapefrom the fuel passages 14 it is not necessary that the joints 15 be gastight. It will be sufficient if the flow resistance through the joint issimilar to that through the exit sheet 12 so that a satisfactorily evenfuel distribution is obtained.

As is indicated in FIG. 2 the thin cross-section of the burner meansthat the flow of air tends to diverge over the exit sheet 12 afterpassing through the air holes 10 and similarly the gas flow through theexit sheet 12 tends to diverge over the air holes 10. This gas flowpattern encourages mixing of air and fuel and hence it facilitatescombustion.

The burner shown in FIGS. 1 and 2 is capable of burning a wide range ofgaseous fuels, e.g., low flame speed fuels such as methane, ethane,propane and bu- .tane as well as high flame speed fuels such ashydrogen.

In all cases combustion takes place with silent, blue flames by adiffusion mechanism. Combustion is complete within about 15 mm, usuallywithin about 5 mm, of the top face of the burner, making it possible tomount a heat exchanger about 25 mm from the top face of the burner togive compact central heating appliances. Thus an appliance ofrectangular cross section 15 cm X 30 cm and 10 12 cm high from thebottom of the burner to the top of the heat exchanger gave a heat outputof 25 kw transferred to the water. (Note this power output is limited bythe need to keep the exit gases above their dew point.)

I claim:

1. A burner for gaseous fuels, which burner is less than 10 mm thick andcomprises a perforated porous exit sheet of metal foam one side of whichis adjacent to a combustion zone and the other side of which is adjacentto a perforated base plate to which the exit sheet is connected in sucha manner that:

a. The perforations in the exit sheet mate with the perforations in thebase plate so as to allow air to pass through them, and

. The exit sheet is spaced apart from the base plate between theperforations so as to form fuel passages whose resistance to the flow offuel gas is low compared with the flow resistance through the exitsheet, the exit sheet being joined to the base plate along the sides ofthe fuel passages so as to prevent excessive escape of gas through thejoints, the whole configuration being such that during the use of theburner gaseous fuel passes throughout 4. A burner according to claim 1,in which the number of perforations is such that they account for 20-50percent of the total area of the burner.

5. A burner according to claim 4, in which the 5 number of perforationsis such that they account for 25-35 percent of the total area of theburner.

ll l 1F

1. A burner for gaseous fuels, which burner is less than 10 mm thick andcomprises a perforated porous exit sheet of metal foam one side of whichis adjacent to a combustion zone and the other side of which is adjacentto a perforated base plate to which the exit sheet is connected in sucha manner that: a. The perforations in the exit sheet mate with theperforations in the base plate so as to allow air to pass through them,and b. The exit sheet is spaced apart from the base plate between theperforations so as to form fuel passages whose resistance to the flow offuel gas is low compared with the flow resistance through the exitsheet, the exit sheet being joined to the base plate along the sides ofthe fuel passages so as to prevent excessive escape of gas through thejoints, the whole configuration being such that during the use of theburner gaseous fuel passes throughout the fuel passages and thence viathe porous exit sheet into the combustion zone where it burns with airdrawn through the perforations.
 2. A burner according to claim 1, inwhich the burner is less than 5 mm thick.
 3. A burner according to claim1, in which the perforations are circular and have an area of 0.01 - 1cm2.
 4. A burner according to claim 1, in which the number ofperforations iS such that they account for 20-50 percent of the totalarea of the burner.
 5. A burner according to claim 4, in which thenumber of perforations is such that they account for 25-35 percent ofthe total area of the burner.